The invention relates to an optical separator of polarizations and to its application to a display system.
More particularly, the invention relates to an optical component with a small thickness but a large surface area, having the function of polarizing an incident wave coming from a source of coherent light (such as a halogen lamp or arc lamp for example). The component obtained can be integrated especially into an optical configuration of a video projection system, and the invention therefore also relates to a display system, notably a liquid crystal display system.
A Bragg mirror is shown in cross-section in FIG. 1. FIG. 1 shows a Bragg mirror comprising a polarizer for the incident wave, the Bragg angle .theta..sub.B =45.degree. at the wavelength .lambda. being also the incidence of the Brewster angle at the interface I between layer with indices of refraction n; n+.DELTA.n. The wave reflected by this component is polarized perpendicularly (as indicated by the conventional polarization symbol, , overlying the arrow pointing along the reflected wave propagation direction), while the transmitted wave is located in the plane of incidence. In its standard form, the component is constituted by two 45.degree. prisms that both have an index of refraction with the value of n. These prisms are attached to a holographic component. The holographic component is recorded by ancillary means on a material with photoinduced index variation. This "polarization-separating prism" fulfils a major optical function in a video projector by integrating liquid crystal active matrices. Original optical architectures making use of the properties of polarization and selective diffraction in wavelength, of these components, are the object of the French patent application No. 90 14620. In certain optical configurations, the optical separating cube may have a size equivalent to the LCD screen (10.times.10 cm.sup.2 typically) which means making a glass or plastic component that is large-sized, hence heavy and bulky.
The invention enables the making of a separator of polarizations that has a small thickness and is hence lightweight and occupies little space.